The method of controlled cooling hot rolled steel rod by forced air cooling, known as the "Stelmor Process" is in successful extensive use throughout the world. It is described generally in the McLean et al U.S. Pat. No. 3,231,432 and involves direct coiling of hot rolled steel rod onto an open conveyor in spread-out rings and, as it is moved along the conveyor, rapidly cooling it by high velocity air streams delivered through nozzles from a plenum supplied with air from a high powered blower. It has been recognized that the quality of the rod produced by the Stelmor Process could, in some cases, be improved if one aspect of the process could be improved. This aspect which, despite much effort has eluded an adequate solution, arises from the tendency of the centers of the rings to cool at a rate which is approximately 25% faster than that of the edges of the rings. This effect is due, at least partly, to the heat shielding effect which the more closely spaced ring edges produce on each other.
One attempt at solving the problem has been to increase the relative areas of the edge and center nozzles so as to force a greater amount of air against the edges of the rings than against their centers. This method still exhibits a difference in the rod cooling rates between the edges and the centers. Another attempt has been to blow high velocity air across the rings from both sides as well as to flow air up through the centers of the rings. In this case, also, the desired degree of predetermined uniform cooling could not be reached.